Several processes have been proposed or used commercially for the removal of color bodies from mixed polyamine products; these processes encompass both physical and chemical methods.
U.S. Pat. No. 3,723,529 discloses a process for the removal of color bodies which comprises treatment of the polyamine with activated carbon at elevated temperatures, 200.degree.-280.degree. C., and subsequent removal, preferably by filtration, of the activated carbon. The resultant polyamine mixture would then be distilled into the desired cuts.
U.S. Pat. No. 4,347,381 discloses a process for the removal or elimination of a pink color content from long chain alkyl amines by treating such products with a trace amount of a bleaching agent. Optionally, the bleaching agent treated amine product can then be heated for a short period of time to improve effectiveness of the bleaching.
U.S. Pat. No. 4,487,987 discloses a method of eliminating color-causing impurities in mixtures of aminoethylpiperazine, polyoxypropylenediamines and alkylphenols by treatment with N,N-diethylhydroxylamine. Quantities on the order of 20 to 500 ppm are effective and the decolorization reaction is conducted at a temperature in the range of about 25.degree. to 50.degree. C.
U.S. Pat. No. 4,567,303 discloses a process for the preparation of colorless alkanolamines in which the process is carried out in a reactor system which is constructed of substantially nickel-free steel. The patent teaches that it is the presence of nickel in the steel walls of the reactor system which causes the color bodies to form, therefore elimination of the nickel in the reactor system produces colorless alkanolamines.
U.S. Pat. No. 4,570,019 discloses a process which can be run continuously for producing polyethylene polyamines having improved color characteristics. The process encompasses treating the discolored polyethylene polyamines with polyethylene polyamine hydrochloride in the presence of water at elevated temperatures for the time necessary to reduce the color of the polyethylene polyamines and then flashing the mixture to evaporate the decolorized polyethylene polyamines from the treating mixture.
Japanese Patent Application No. 39-27478 discloses a process for decolorizing ethylene amines characterized in that at least one metal from among zinc, aluminum, and tin and at least one alkali selected from sodium hydroxide and potassium hydroxide are added to the discolored amines and heated.
Japanese Patent Application No. 40-1330 discloses a process for decolorizing polyethylene polyamines by bringing the discolored polyamine into intimate contact with zinc and water at room temperature to about 150.degree. C.
Japanese Patent Application No. 43-53148 discloses a process for decolorizing ethylene amines by adding zinc to the colored ethylene amine followed by heating.